1. Field of the Invention
The present invention relates to a digital still camera with a flash device.
2. Background Arts
A digital still camera has a white balance adjustment function to correct the color balance of an image taken under various light sources. For example, since a main subject illuminated by flashlight even under illumination of an artificial light source, a taken image is usually subject to color balance correction by use of a prescribed adjustment value for the flashlight.
However, when available light, such as illumination light from the artificial light source, is strong or when the flashlight is weak, the main subject is influenced by available light. As a result, the color balance of the taken image becomes undesirable.
In order to obtain the image with desirable white balance, an attempt has made to determine a correct adjustment value for white balance correction by obtaining the ratio of the flashlight to available light illuminated on the main subject.
In order to calculate the ratio, however, it is necessary to obtain much information, such as the distance between the digital still camera and the main subject, the position of the main subject, brightness of the main subject, the amount of the flashlight, and the like. A digital still camera with sensors to obtain such information is very expensive.
Some digital still camera sets the adjustment value such that the corrected value is slightly smaller than that in photography without the flashlight. In that case, however, since such adjustment value is not proper to correct the white balance, the main subject in the taken image tends to have undesirable color.
For the purpose of solving the above problem, Japanese Patent Laid-Open Publication No. 11-298908 describes an image processing method in which a subject exposure with the flashlight and a background exposure with the available light are carried out in a single photography. In the subject exposure, the digital camera emits flashlight to illuminate the main subject with the correct brightness. The white balance of the subject image is adjusted by the adjustment value for the flashlight. In the background exposure, an exposure is carried out with available light, and the white balance of the background image is adjusted by the adjustment value for available light. Then, both images are synthesized to obtain a composite image in which the white balance of the main subject and the background are properly adjusted.
However, in the above image processing method, it is presumed that the main subject is extremely dark compared to the background. When brightness of the main subject is not largely different from brightness of the background, it is difficult to remove an influence of available light on the main subject. Moreover, the main subject in the taken image tends to be overexposed because of the flashlight and available light illuminated on the main subject. Accordingly, the image processing method is not applicable to indoor photography.